Gradually rolling out eslint rules resulting in many errors in a legacy project

check-for-legacy-headers.js

/*
This script is meant to be used with lint-staged receiving changed files as arguments.
It checks if file has "rules-disabled-on" header present with date in the past.
If yes, it reports files that need to be reformatted.
*/

const _ = require('lodash')
const fs = require('fs')
const moment = require('moment')

const errors = []

process.argv.slice(2).forEach(filepath => {
  const lines = fs.readFileSync(filepath, 'utf8').split('\n')
  const rulesDisabledPattern = /^\/\* rules-disabled-on ([0-9-]+) \*\/$/
  const rulesDisabledLineIndex = _.findIndex(lines, line => rulesDisabledPattern.test(line))
  if (rulesDisabledLineIndex === -1) {
    return
  }
  const date = rulesDisabledPattern.exec(lines[rulesDisabledLineIndex])[1]
  if (moment().format('YYYY-MM-DD') === date) {
    return
  }

  const ruleLinePattern = /^\/\* eslint-disable ([^ ]+) \*\/$/
  const rules = lines
    .slice(0, rulesDisabledLineIndex)
    .filter(line => line.trim())
    .map(line => ruleLinePattern.exec(line))
    .map(m => m && m[1])
    .filter(_.identity)

  errors.push({ filepath, rules })
})

const formatError = ({ filepath, rules }) => [`${filepath}:`, ...rules.map(rule => `\t${rule}`)].join('\n')

if (errors.length) {
  const rulesReport = errors.map(formatError).join('\n\n')
  // eslint-disable-next-line no-console
  console.error(`Legacy disabled eslint rules found in:

${rulesReport}
  
Remove disabled rules and fix the issues before committing!

`)

  process.exit(1)
}

process.exit()

ignore-eslint-errors.js

/*
This script prepends all JS files containing eslint errors with a header like this:
*/

/* eslint-disable func-names */
/* eslint-disable no-underscore-dangle */
/* eslint-disable no-fallthrough */
/* rules-disabled-on 2019-11-11 */

/*
Run the script from the root of the project directory.
Pass eslint errors JSON file as argument.
Save errors in JSON by running `eslint --format=json-with-metadata`
*/

const { map, filter, orderBy, flow } = require('lodash/fp')
const fs = require('fs')
const path = require('path')
const moment = require('moment')

const errorJSONFilePath = process.argv[2]

const errors = JSON.parse(fs.readFileSync(path.resolve(__dirname, errorJSONFilePath), 'utf8')).results

const getFilesWithErrors = flow(
  filter((d) => d.errorCount + d.warningCount > 0),
  map(({ filePath, messages }) => {
    const rules = messages.reduce((acc, { ruleId }) => {
      acc.add(ruleId)
      return acc
    }, new Set())
    return { filePath, rules }
  }),
  orderBy([(d) => d.rules.size], ['desc'])
)

const constructHeaderFactory = (dateToday) =>
  flow(
    (rules) => rules.map((rule) => `/* eslint-disable ${rule} */`),
    (lines) => [...lines, `/* rules-disabled-on ${dateToday} */`],
    (lines) => lines.join('\n')
  )

const constructHeader = constructHeaderFactory(moment().format('YYYY-MM-DD'))

const prependFile = (txt, filePath) => {
  const content = fs.readFileSync(filePath, 'utf8')
  fs.writeFileSync(filePath, `${txt}${content}`)
}
console.log('files with errors', getFilesWithErrors(errors))

// eslint-disable-next-line no-restricted-syntax
for (const file of getFilesWithErrors(errors)) {
  const { filePath, rules } = file
  const header = constructHeader(Array.from(rules))
  prependFile(`${header}\n\n`, filePath)
  // eslint-disable-next-line no-console
  console.log('wrote', filePath)
}

lint-staged.config.js

const formatAndLint = ['node scripts/check-for-legacy-headers.js', 'prettier --write', 'eslint --max-warnings 0 --fix']

module.exports = {
  '*.graphql': 'prettier --write',
  // unfortunately, tsc cannot be run for specific files and still respect tsconfig :'(
  '*.{ts,tsx}': [...formatAndLint, () => 'yarn tsc -p ./tsconfig.json --noEmit'],
  '*.{js,jsx}': [...formatAndLint],
}